.middle{
    width: 90%;
    margin: 20px auto;
}

.middle ul{
    display: flex;
    flex-wrap: wrap;
    justify-content: space-around;
}

.middle ul li{
    width: 300px;
    height: 200px;
    margin: 20px;
    border: 1px dashed darkblue;
    text-align: center;
    line-height: 100px;
    cursor: pointer;
}

.middle ul li:hover{
    background: gainsboro;
}